In the past, high-performance missile configurations have been constrained almost exclusively to bodies of revolution employing cruciform control. The desire to utilize the higher maneuver-duty-cycle capability (g-sec) of lifting bodies presents the problem of controlling their nonlinear, cross-coupled motions. The unique feature of lifting-body control is the requirement to align one missile-maneuver plane with the desired inertial-maneuver direction. Hence, high-performance roll maneuvers are required that meet such criteria as time response, etc. Cruciform control techniques using arbitrary maneuver directions are obviously not suitable for lifting bodies where the high-lift missile plane must be used for efficient maneuver performance.
Some problems in lifting-body control design are: (1) crosscoupling terms are difficult to suppress and are sometimes destabilizing, (2) nonlinearities make conventional linear design procedures less valid, and (3) to meet response-time criteria, roll-control torque requirements may be quite large. The roll-torque penalty is striking if required roll capability for cruciform and lifting-body control are compared on a configuration suited for cruciform control. For typical lifting bodies, a reduced yaw-control requirement and increased rollmoment arm tend to reduce the total control-force penalty.
The cross-coupling phenomena may be divided into four categories, according to source: (1) geometric, (2) gyroscopic, (3) control induced, and (4) aerodynamic. Categories 1 and 2 are important because of high roll rates. Categories 3 and 4 are configuration dependent. Of particular interest in terms of performance is yaw/roll aerodynamic coupling. Without proper yaw-autopilot maneuver strategy, roll-maneuver time is significantly increased by this phenomenon.